(1) Field of the Invention
The present invention relates to a packet forwarding apparatus and, more particularly, to a system configuration for extending the function of the packet forwarding apparatus.
(2) Description of Related Art
A packet communication network such as an IP network is composed of a plurality of packet forwarding apparatus for relaying packets. A packet transmitted from a terminal device reaches destination terminal equipment or a server via these packet forwarding apparatuses. Each of the packet forwarding apparatus refers to a routing table in accordance with a destination address included in the header of an ingress packet received from each of input lines and specifies an output line onto which the ingress packet is to be forwarded. After performing a proper updating process with respect to the header information of the ingress packet, the packet forwarding apparatus transmits the ingress packet to the next packet forwarding apparatus via the specified output line.
There are restraints on the ability of a conventional packet forwarding apparatus to process ingress packets. When the processing ability needs to be greatly modified, it is necessary to replace the whole packet forwarding apparatus with a new apparatus. Since the replacement with the new packet forwarding apparatus requires a large equipment investment, it becomes difficult to frequently change the network function in compliance with user needs.
As one solution to the above problem, it is practical to design such a structure that allows the function of a packet forwarding apparatus to be extended to a degree so as to partly modify the packet forwarding apparatus or add a new functional board thereto when necessity demands. For example, Japanese Unexamined Patent Publication No. 2002-281072 (US 2002/0150088 A1: Patent Document 1) proposes an inter-network apparatus and an inter-network method that enable functional extension by replacing a network interface card connected to the internal switch of a packet forwarding apparatus with a functional extension card.
In accordance with the extension system proposed in Patent Document 1, however, it is necessary to newly develop hardware for the network interface to be connected to the maker-specific internal switch provided in the packet forwarding apparatus and to perform a component exchange with an existing packet forwarding apparatus. Although this system is lower in cost than in the case where the whole packet forwarding apparatus is replaced with a new model, the provision of the new interface board demands an expert understanding on the hardware of the packet forwarding apparatus so that the design and prototyping of the hardware requires still high cost. In addition, there are also size-related constraints on the new interface board for the replacement of an existing board therewith.